The present invention relates generally to a swivel seat for a vehicle. More specifically, the invention relates to a swivel seat pivotable between a normal frontwardly directed position and a pivoted position directed toward a door opening for convenience of entry into and exit from the vehicle.
Conventionally, some types of vehicles employ swivel seats or rotatable seats. Those swivel or rotatable seats are pivotable or rotatable generally about a central, vertical pivot axis. Pivot mechanisms enable these seats to rotate.
The pivot mechanism generally comprises a stationary base, a pivotal seat cushion frame and a pivot axle projecting from the stationary base and pivotably or rotatably supporting the pivotal seat cushion frame. One or more roller assemblies between the stationary base and the pivotal seat cushion frame allow smooth pivotal movement or rotation of the seat cushion frame relative to the stationary base. A locking mechanism locks the seat in its normal, forward-facing position.
In such swivel or rotatable seats, the pivot axle and roller or rollers have to support the weight of the seat assembly which comprises a seat cushion and a seat back as well as that of the occupant of the seat. Therefore, the load on the pivot axle and the roller or rollers is relatively high. In addition, the load due to the weight of the occupant is not necessarily distributed evenly over the seat. An uneven load exerted on the seat may tend to lift either the front or rear edge of the seat. This uneven load is thus manifested as a distorting force on the pivot axle, the locking mechanism and the roller or rollers. Since conventional swivel seats have no way to prevent the front or rear edge of the seat from raising due to uneven load, the pivot axle, the locking mechanism and/or the roller or rollers are subject to distorting forces which shorten its service life and degrade durability.
In addition, the roller or rollers must be strong enough to withstand the heaviest possible instantaneous load, which arises when the occupant sits down. This enforces an increased roller area. Increased roller size leads to the problem of differential of radius of curvature between the parts of the roller nearest to and farthest away from the central pivot axis, which implies differential rates of rotation. As a result, the roller must slip to allow smooth pivotal rotational movement of the seat cushion frame relative to the stationary base. This slip results in disturbing noise.